Batteries based on lithium (Li), such as lithium-ion batteries, are attractive due to their high energy density compared to other commercial batteries. Li-ion batteries are used commercially in computers, cell phones, and related devices. Li-ion batteries have potential for use in electric vehicle/hybrid-electric vehicle (EV/HEV) applications. The most-suitable battery technology, which offers both a sufficient range and enough power to provide the acceleration required by today's drivers, is the lithium-ion battery system (Grove and Burgleman, The McKinsey Quarterly, December 2008).
In recent years, commercial efforts have attempted to improve lithium-ion batteries to meet the requirements demanded for target applications. Particularly for EV/HEV applications, high charge and discharge rates across a large temperature range (e.g., −30° C. to 60° C.) and long cycle life are critical requirements. Presently, these requirements have not been met. To date, a major technological bottleneck limiting the operation of Li-ion batteries over a wide temperature range is the electrolyte.
In a typical Li-ion battery, the Li+ cation moves from the anode to the cathode (discharging) or cathode to anode (charging). The electrolyte is normally a lithium salt in a non-aqueous solvent. Electrolyte additives are known in the art which possess specific properties to enhance battery function. Electrolyte additives are generally beneficial at either low or high temperature, but not across a wide range of temperatures. Typically, such additives exhibit specific functions to enhance battery discharge capacity and cycling stability. Some additives work very well for low temperatures but not at high temperatures, while other additives perform well at high temperatures but not at low temperatures.
In light of these and other shortcomings in the art, improved electrolyte additives are needed for Li-ion batteries. Improved electrolyte additives preferably minimize the battery performance gap between low and high temperatures, maintaining good function and cycle stability throughout a range of practical operation temperatures. What is particularly desired are electrolyte additives that are selected or designed to be effective at any practical temperature, by employing at least two different temperature-dependent chemical mechanisms suitable to confer benefits to battery performance.